The present disclosure relates generally to the optical network field, and more particularly to a PON system and method for protecting its services.
A Passive Optical Network, or PON, is an optical fiber cabling network accessed by a user in which the central part contains no active electronic devices and all of the user signals converge going upstream and are broadcast going downstream using only passive components, such as optical dividers. Passive optical network technology is a broadband access technology that has great competitive advantages and is an important technical means that offers user access over the “the last mile”. By using passive optical components in its optical distribution network (ODN) and optical fiber as the medium for transmission, the technology has the advantages of high bandwidth, high immunity to electromagnetic interference, low loss, low cost, and simple design. In recent years, various PON technologies have gradually become commercially available.
Referring to FIG. 1, most existing optical network systems adopt a tree topology. User services access the network through an optical network unit (ONU) or an optical network terminal (ONT), are pooled on the ODN, and are ultimately sent to an optical line terminal (OLT). However, a pure tree topology does not have measures for failure protection and recovery or means for locating a failure. If an equipment or link fault is not corrected for a long time, the user services may be greatly affected and security may be seriously impaired. It is also very difficult to locate the fault. Therefore, the security of the PON is an issue of great importance and the PON must be capable of protecting its services in the event that it has a fault.
The existing PON systems achieve service protection by means of fully-protected optical fiber switchover, as shown in FIG. 2. In such a system, there are two links between the OLT and the ODN, and between the ONU and each ONU/ONT, where one link serves as redundancy backup to ensure a quick recovery of services in case of a fault.
However, the existing failure protection measures achieve unobstructed network traffic and normal services by adding a large number of redundant equipment and have the following defects:                1. High construction cost. Each ONU requires two sets of identical transmission equipment requires an additional optical interface, which results in a dramatic increase in the ONU cost.        2. Low bandwidth utilization. Only one of the two work channels is working while the other one is always idle, resulting in an increased waste of resources.        3. Inability to locate a fault and indicate fault type.        